A modified sealing material based on polyphenylene sulfide and a method for preparing the same

Abstract

This invention relates to the field of polymer materials technology, specifically to a modified sealing material based on polyphenylene sulfide (PPS) and its preparation method. This invention overcomes the problems of poor mechanical properties and poor thermal stability of existing sealing materials. In this application, PPS resin, nano-hexagonal boron nitride, calcium pimecronate, and a composite antioxidant are mixed to obtain a premix. This premix, PPS-grafted maleic anhydride, modified silica fume, and modified glass fiber are added stepwise through a twin-screw extruder, followed by extrusion granulation. Finally, variable mold temperature injection molding is used, with the mold temperature rising and then rapidly cooled during the filling stage to obtain the modified sealing material. This invention constructs a microscopic synergistic reinforcing network through a flexible polydopamine layer and a rigid inorganic phase, supplemented by rapid heating and cooling injection molding to eliminate residual internal stress and induce uniform and rapid crystallization of PPS, significantly improving the mechanical strength, fatigue life, and thermal stability of the molded part.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a modified sealing material based on polyphenylene sulfide and its preparation method. Background Technology

[0002] In the field of precision polymer material processing, polyphenylene sulfide (PPS) is the preferred substrate for preparing high-performance thin-walled precision parts due to its excellent chemical resistance, flame retardancy, and thermal stability. However, PPS resin has inherent defects in its crystallization behavior, with a relatively slow crystallization rate. When processing parts with thin-walled dimensions and high precision requirements, the slow crystallization process easily leads to uneven melt flow and inconsistent cooling shrinkage, resulting in severe internal stress accumulation and warping deformation. Currently, although cold injection molding can alleviate deformation to some extent, it often results in insufficient final crystallinity of the material, failing to realize its full physicochemical properties. To compensate for this defect, a long-duration, energy-intensive secondary annealing process is usually required, which not only reduces production efficiency but also increases the risk of material property fluctuations.

[0003] Besides processing bottlenecks, the structural stability of polyphenylene sulfide (PPS) materials during high-temperature service and thermal processing also faces significant challenges. PPS is highly susceptible to thermo-oxidative aging reactions during high-temperature molten processing, especially when it remains in the barrel for extended periods. This oxidative degradation process leads to irreversible breakage or cross-linking of the polymer molecular chains, significantly weakening the material's intrinsic mechanical properties, manifesting as decreased toughness, increased brittleness, and shortened dynamic fatigue life. Under the complex mechanical environment of high temperature, high pressure, and continuous friction, conventional PPS-modified materials often suffer from insufficient thermomechanical fatigue resistance, easily developing microcracks and accompanied by severe mechanical wear, making it difficult to meet the stringent requirements of high-end industrial applications for the service stability and high sealing reliability of polymer composite materials.

[0004] To address this, a modified sealing material based on polyphenylene sulfide and its preparation method are proposed. Summary of the Invention

[0005] The purpose of this invention is to design a modified sealing material based on polyphenylene sulfide (PPS) and its preparation method. This invention involves mixing PPS resin, nano-hexagonal boron nitride, calcium pimecrolate, and a composite antioxidant to obtain a premix. This premix, along with PPS grafted maleic anhydride, modified silica fume, and modified glass fiber, are added in stages via a twin-screw extruder, followed by extrusion granulation. Finally, variable mold temperature injection molding is used, with the mold temperature rising and then rapidly cooled during the filling stage to obtain the modified sealing material. This invention constructs a microscopic synergistic reinforcing network through a flexible polydopamine layer and a rigid inorganic phase, and utilizes rapid heating and cooling injection molding to eliminate residual internal stress and induce uniform and rapid crystallization of PPS, significantly improving the mechanical strength, fatigue life, and thermal stability of the molded part.

[0006] To achieve the above objectives, the present invention provides the following technical solution: Unless otherwise specified, all the following parts are by weight.

[0007] This invention provides a method for preparing a modified sealing material based on polyphenylene sulfide, the method comprising the following steps:

[0008] Polyphenylene sulfide resin, hexagonal boron nitride, calcium pimecronate, and a composite antioxidant are mixed to form a premix. The premix, polyphenylene sulfide-grafted maleic anhydride, modified silica fume, and modified glass fiber are added stepwise to a twin-screw extruder, extruded, water-cooled, pelletized, and vacuum-dried to obtain modified polyphenylene sulfide granules. The modified polyphenylene sulfide granules are then melt-plasticized and injection-molded to obtain a modified sealing material. Polyphenylene sulfide-grafted maleic anhydride is obtained by grafting maleic anhydride onto polyphenylene sulfide. Modified silica fume is obtained by modifying silica fume with a silane coupling agent. Modified glass fiber is obtained by modifying glass fiber with polydopamine.

[0009] Preferably, the modified glass fiber is prepared as follows: 95-105 parts of chopped glass fiber (fiber diameter 10-13 μm, length 3-4 mm) are placed in a muffle furnace and calcined at 400℃-450℃ for 2 hours to remove industrial wetting agents and organic impurities from the surface; after cooling, it is immersed in 0.1 mol / L dilute hydrochloric acid and ultrasonically treated for 10 minutes, washed with deionized water until neutral, and dried at 80℃ to obtain activated glass fiber; 500 parts of deionized water are added to a reaction vessel, and 1 part of tris(hydroxymethyl)aminomethane is added. Alkane was stirred and dissolved, and 0.1 mol / L dilute hydrochloric acid was added dropwise to adjust the pH of the solution to 8.5 to prepare a buffer solution. The activated glass fiber was completely immersed in the buffer solution, and 1-3 parts of dopamine hydrochloride were added. The reaction was carried out at room temperature (25°C) and fully exposed to air (to provide oxygen) for 14 hours with slow stirring at 200 rpm. After the reaction was completed, the solid was filtered out, washed 4 times alternately with deionized water and anhydrous ethanol, and placed in a vacuum drying oven to be vacuum dried at 80°C for 6 hours to obtain modified glass fiber.

[0010] Preferably, the modified silica fume is prepared as follows: 95-105 parts of silica fume are added to 450 parts of a mixed solvent of ethanol and water (where the volume ratio of anhydrous ethanol to deionized water is 95:5), and ultrasonically dispersed for 30 min (ultrasonic frequency 40 kHz) to form a suspension; then 1-3 parts of KH-550 (γ-aminopropyltriethoxysilane) are slowly added dropwise to the suspension, and the mixture is refluxed for 4 h under constant temperature water bath (65℃) with mechanical stirring (400 rpm). After the reaction is completed, the solid product is obtained by centrifugation, washed 3 times with anhydrous ethanol, dried in a vacuum drying oven at 100℃ for 4 h, and ground through a 250-mesh sieve to obtain the modified silica fume.

[0011] Preferably, the preparation method of polyphenylene sulfide grafted with maleic anhydride is as follows: At room temperature (25°C), 2-3 parts of maleic anhydride powder are added to 3 parts of styrene, and 0.15 parts of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane are added, and the mixture is stirred for 20 minutes (300 rpm) to obtain a mixed solution; 100 parts of polyphenylene sulfide powder (average particle size of 50-100 μm) that has been vacuum dried at 120°C for 4 hours and 0.3 parts of ethylene bis-stearamide are added to a high-speed mixer, the mixer is started (low speed 300 rpm), and the mixed solution is evenly sprayed onto the powder surface using a high-pressure atomizing nozzle. After spraying, the speed is increased to 800 rpm for high-speed mixing for 5 minutes, and then the mixture is sealed and allowed to stand for 2-4 hours to mature, obtaining a mixed material; the mixed material is then added to the same... A parallel twin-screw extruder (L / D ratio ≥ 45, screw assembly includes two high-shear kneading block sections and one deep-groove venting section) is used. The feeding section is set at 150℃ (to prevent feed back and premature monomer volatilization), the melt reaction section is set at 280℃-290℃-305℃, and the venting section and die head are set at 295℃. The screw speed is 280 rpm. In the middle and rear section of the extruder, a high-intensity vacuum venting system is activated (vacuum degree maintained at -0.09MPa to -0.098MPa). The extruded strip is passed through a water tank (water temperature controlled at 60℃ to avoid rapid cooling that would cause the strip to become brittle and break), dried by a powerful air knife, and then sent to a pelletizer for pelleting. After being vacuum dried at 100℃ for 2 hours, polyphenylene sulfide grafted maleic anhydride with a grafting rate of 1.0%-1.5% is obtained.

[0012] Preferably, the modified sealing material is prepared as follows: 1.5 parts of nano-hexagonal boron nitride (average particle size 50-100 nm), 0.5 parts of calcium pimecronate, and 0.5 parts of ethylene bis-stearamide are added to a high-speed mixer and subjected to high-speed friction mixing at 2500 rpm for 3 min; then 98-102 parts of polyphenylene sulfide resin (melt index (MFR) ≥ 100 g / 10 min) and 0.6 parts of composite antioxidant are added, and the mixing speed is reduced to 800 rpm at room temperature. Mix for 5 minutes to form a premix. Use a co-rotating parallel twin-screw extruder (L / D ratio ≥ 40, equipped with a side feeding system and a vacuum exhaust system). Add the premix from the main feed port, add 3-5 parts of polyphenylene sulfide-grafted maleic anhydride and 8-10 parts of modified silica fume from the first side feed port, and add 30-35 parts of modified glass fiber from the second side feed port (near the middle and rear section of the extruder). Set the temperature gradient for each zone of the screw: Zone 1 280℃, Zones 2 to 4 300℃-310℃. In zones 5-7, the temperature is 315℃, the die head temperature is 310℃, and the screw speed is 300-350 rpm. The vacuum exhaust system is activated in the extruder exhaust section, maintaining a vacuum of -0.08 MPa to -0.09 MPa to remove moisture and low-molecular-weight volatiles generated during the reaction. The extrudate is cooled in a water bath (water bath temperature controlled at 55℃), dried by an air knife, granulated, and placed in a vacuum drying oven at 80℃ for 2 hours to obtain modified polyphenylene sulfide granules. These modified polyphenylene sulfide granules are then fed into the injection molding machine. The molding machine's barrel temperature is set to 300℃ (rear section) - 315℃ (middle section) - 330℃ (nozzle), the injection pressure is 90MPa, the holding pressure is 55MPa, and the holding time is 4s. During injection molding, superheated water or electromagnetic induction heating is used to raise the mold cavity surface temperature to 150℃ during the injection filling stage. Then, the cooling water circuit (forced cooling water) is switched instantly to make the mold cavity surface temperature drop sharply to 110℃. The cooling time is controlled within 9s. After mold opening and ejection, the modified sealing material is obtained.

[0013] Preferably, the composite antioxidant includes antioxidant 1010 and antioxidant 168, with the weight ratio of antioxidant 1010 to antioxidant 168 being 1:1.

[0014] Another aspect of the present invention provides a modified sealing material based on polyphenylene sulfide, the raw materials for which include polyphenylene sulfide resin, nano-hexagonal boron nitride, calcium pimecronate, polyphenylene sulfide grafted maleic anhydride, modified silica fume, modified glass fiber and composite antioxidant.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1. This invention employs polydopamine to biomimeticly coat glass fibers. Under oxygen-free high temperature, polydopamine undergoes localized intramolecular dehydration, cyclization, and cross-linking reactions, transforming in situ into a dense nitrogen-doped semi-carbonized conjugated network. This not only retains some incompletely converted imine and secondary amino groups to form interfacial bonds with the anhydride groups of maleic anhydride grafted onto polyphenylene sulfide, but also forms a rigid-flexible gradient transition layer between inorganic glass fiber and polyphenylene sulfide resin. This mechanism overcomes the defects of traditional rigid modified polyphenylene sulfide materials, such as brittleness and poor mechanical toughness, significantly extending the fatigue life of seals under complex stresses and preventing micro-cracking.

[0017] 2. This invention utilizes silica fume modified with KH-550 silane coupling agent. During twin-screw reactive extrusion, it undergoes an imidization reaction with the maleic anhydride groups grafted onto polyphenylene sulfide (PPS) maleic anhydride. This chemical bonding constructs an in-situ crosslinked network within the PPS matrix, with micro-nano silica fume as rigid nodes. This network acts like a "skeletal protective suit" for the polymer chains, restricting the thermal motion of PPS molecular chains under high-temperature conditions, significantly improving the material's heat distortion temperature, and solving the problems of poor thermal stability and easy softening failure of sealing materials under high-temperature and high-pressure service conditions.

[0018] 3. Addressing the technical challenge of easy main chain breakage and degradation when maleic anhydride is directly grafted onto polyphenylene sulfide (PPS), this invention introduces styrene as a comonomer during the preparation of PPS grafted with maleic anhydride, employing a special process of atomized spraying and solid-phase swelling curing. The charge-transfer complex formed by styrene and maleic anhydride not only significantly increases the grafting rate of polar groups, but more importantly, the buffering effect of styrene protects the free radicals of the PPS macromolecule, preventing main chain breakage and yellowing degradation. Combined with vacuum devolatilization, the integrity of the high molecular weight of the matrix resin is ensured, laying a solid material foundation for the final material's macroscopic mechanical properties and thermal stability.

[0019] 4. The premix of this invention incorporates antioxidants 1010 and 168. Antioxidant 1010 captures free radicals generated at high temperatures, while antioxidant 168 decomposes hydroperoxides, forming a synergistic defense. Combined with the controlled stepped temperature gradient during extrusion and injection molding, and the side-feeding process (reducing shear heat generation of glass fiber in the high-temperature barrel), the thermo-oxidative degradation reaction of polyphenylene sulfide is effectively suppressed during harsh high-temperature processing and long-term service. This avoids embrittlement and mechanical property degradation caused by thermo-oxidative aging, giving the sealing material excellent long-term thermal stability.

[0020] 5. This invention combines the high in-plane thermal conductivity of nano-hexagonal boron nitride with the heterogeneous nucleation effect of calcium pimecrolate to build a microscopic thermally conductive crystalline network within the material. Simultaneously, a rapid heating and cooling variable-temperature injection molding process is introduced at the molding end. This deep synergy not only eliminates residual flow stress in thin-walled sealing strips during mold filling but also induces uniform deep crystallization of polyphenylene sulfide. The significant increase in crystallinity directly translates into a comprehensive improvement in the material's surface hardness, tensile strength, and heat resistance limit, eliminating the need for traditional secondary annealing processes. Attached Figure Description

[0021] Figure 1 The tensile strength and heat distortion temperature diagrams for embodiments 1-5 of the present invention are shown. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] For details, please refer to [link / reference]. Figure 1 This invention provides a modified sealing material based on polyphenylene sulfide and its preparation method, the technical solution of which is as follows:

[0024] Example 1

[0025] 100 parts of chopped glass fibers were placed in a muffle furnace and calcined at 420℃ for 2 hours. After cooling, they were immersed in 0.1 mol / L dilute hydrochloric acid and sonicated for 10 minutes. They were washed with deionized water until neutral and dried at 80℃ to obtain activated glass fibers. 500 parts of deionized water were added to a reaction vessel, along with 1 part of tris(hydroxymethyl)aminomethane. The mixture was stirred to dissolve and 0.1 mol / L dilute hydrochloric acid was added dropwise to adjust the pH of the solution to 8.5 to prepare a buffer solution. The activated glass fibers were completely immersed in the buffer solution, and 2 parts of dopamine hydrochloride were added. The mixture was stirred slowly at 200 rpm for 14 hours at room temperature (25℃) and under full exposure to air. After the reaction, the solid was filtered out and washed 4 times alternately with deionized water and anhydrous ethanol. The solid was then placed in a vacuum drying oven and dried under vacuum at 80℃ for 6 hours to obtain modified glass fibers.

[0026] 100 parts of silica fume were added to 450 parts of a mixed solvent of ethanol and water (the volume ratio of anhydrous ethanol to deionized water was 95:5), and ultrasonically dispersed for 30 min (ultrasonic frequency 40 kHz) to form a suspension. Then, 2 parts of KH-550 were slowly added dropwise to the suspension, and the mixture was refluxed for 4 h under constant temperature water bath (65℃) with mechanical stirring (400 rpm). After the reaction was completed, the solid product was obtained by centrifugation, washed 3 times with anhydrous ethanol, dried in a vacuum drying oven at 100℃ for 4 h, and ground through a 250-mesh sieve to obtain modified silica fume.

[0027] At room temperature (25℃), 2.5 parts of maleic anhydride powder were added to 3 parts of styrene, along with 0.15 parts of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane. The mixture was stirred for 20 minutes (300 rpm) to obtain a mixed solution. 100 parts of polyphenylene sulfide powder that had been vacuum dried at 120℃ for 4 hours and 0.3 parts of ethylene bis-stearamide were added to a high-speed mixer. The mixer was started (low speed 300 rpm), and the mixed solution was evenly sprayed onto the powder surface using a high-pressure atomizing nozzle. After spraying, the speed was increased to 800 rpm for high-speed mixing for 5 minutes, followed by a sealed static mixing process. After aging for 3 hours, a mixture was obtained. The mixture was then fed into a co-rotating parallel twin-screw extruder. The feeding section was set to 150°C, the melting reaction section to 280°C-290°C-305°C, and the exhaust section and die head to 295°C. The screw speed was 280 rpm. In the middle and rear section of the extruder, a high-intensity vacuum exhaust system was turned on (vacuum degree maintained at -0.09MPa to -0.098MPa). The extruded strip was passed through a water tank (water temperature controlled at 60°C), dried by a powerful air knife, and then sent to a pelletizer for pelleting. After being vacuum dried at 100°C for 2 hours, polyphenylene sulfide grafted maleic anhydride was obtained.

[0028] The compound antioxidant includes antioxidant 1010 and antioxidant 168, with a weight ratio of antioxidant 1010 to antioxidant 168 of 1:1.

[0029] 1.5 parts of nano-hexagonal boron nitride, 0.5 parts of calcium pimecronate, and 0.5 parts of ethylene bis-stearamide were added to a high-speed mixer and subjected to high-speed friction mixing at 2500 rpm for 3 minutes. Then, 100 parts of polyphenylene sulfide resin and 0.6 parts of composite antioxidant were added, and the mixing speed was reduced to 800 rpm at room temperature for 5 minutes to form a premix. A co-rotating parallel twin-screw extruder was used. The premix was added from the main feed port, 4 parts of polyphenylene sulfide grafted maleic anhydride and 9 parts of modified silica fume were added from the first side feed port, and 32 parts of modified glass fiber were added from the second side feed port (near the middle and rear section of the extruder). The screw temperature gradient was set as follows: Zone 1 280℃, Zones 2-4 305℃, Zones 5-7 315℃, die head temperature 310℃, screw speed 320 rpm, and vacuum exhaust system was activated in the extruder exhaust section. The system maintains a vacuum level of -0.08MPa to -0.09MPa to remove moisture and low-molecular-weight volatiles generated during the reaction. The extrudate is cooled in a water bath (water bath temperature controlled at 55℃), dried by an air knife, granulated, and placed in a vacuum drying oven at 80℃ for 2 hours to obtain modified polyphenylene sulfide granules. The modified polyphenylene sulfide granules are then fed into an injection molding machine. The barrel temperature is set as follows: 300℃ (rear section) - 315℃ (middle section) - 330℃ (nozzle). The injection pressure is 90MPa, the holding pressure is 55MPa, and the holding time is 4s. During injection molding, superheated water or electromagnetic induction heating is used to raise the mold cavity surface temperature to 150℃ during the injection filling stage. Then, the cooling water path is switched instantly to cause the mold cavity surface temperature to drop sharply to 110℃. The cooling time is controlled at 9s. The mold is then opened and the material is ejected to obtain the modified sealing material.

[0030] Examples 2-5 refer to the parameter conditions in Example 1, with specific differences shown in Table 1.

[0031] Table 1 Parameters and conditions for Examples 1-5

[0032] Key process parameters Example 1 Example 2 Example 3 Example 4 Example 5 Dosage of chopped glass fiber / portion 100 95 98 102 105 Calcination temperature / °C 420 400 410 440 450 Dosage / part of dopamine hydrochloride 2 1 3 3 1 Dosage of silica fume (per serving) 100 95 98 102 105 Dosage of KH-550 / serving 2 1 1 3 3 Dosage / parts of maleic anhydride powder 2.5 2 3 2 3 resting and ripening time / h 3 2 2.5 3.5 4 Dosage / parts of polyphenylene sulfide resin 100 98 99 101 102 Dosage / parts of polyphenylene sulfide grafted maleic anhydride 4 3 5 3 5 Dosage of modified silica fume (parts) 9 8 8 10 10 Dosage of modified glass fiber / parts 32 30 31 34 35 Temperature in zones two through four / °C 305 310 300 300 310 Screw rotation speed / rpm 320 300 310 330 350

[0033] Comparative Example 1 follows the same parameters and conditions as in Example 1, except that the glass fiber is not modified.

[0034] Comparative Example 2 follows the same parameters and conditions as in Example 1, except that no modified glass fiber is added.

[0035] Comparative Example 3 follows the same parameters and conditions as in Example 1, except that no modification treatment is applied to the silica fume.

[0036] Comparative Example 4 follows the same parameters and conditions as in Example 1, except that no modified silica fume is added.

[0037] Comparative Example 5 follows the same parameters and conditions as in Example 1, except that no styrene monomer is added when preparing polyphenylene sulfide grafted with maleic anhydride.

[0038] Comparative Example 6 follows the same parameters and conditions as in Example 1, except that maleic anhydride is used instead of polyphenylene sulfide grafted with maleic anhydride.

[0039] Comparative Example 7 follows the same parameters and conditions as in Example 1, except that nano-hexagonal boron nitride is not added.

[0040] Comparative Example 8 follows the same parameters and conditions as in Example 1, except that no composite antioxidant is added.

[0041] Comparative Example 9 follows the same parameters and conditions as in Example 1, except that modified glass fiber and premixed materials such as polyphenylene sulfide resin are added together from the main feed port of a twin-screw extruder.

[0042] Comparative Example 10 uses the same parameters as in Example 1, except that hot water or electromagnetic induction heating and instantaneous cooling water are not used during injection molding. Instead, conventional constant mold temperature injection is used (the mold temperature is constant at 130°C throughout the process).

[0043] Experimental Example 1: Mechanical Properties and Thermal Stability Testing

[0044] The tensile strength of Examples 1-5 and Comparative Examples 1-7 was tested according to the test method of ISO 527; the flexural modulus of Examples 1-5 and Comparative Examples 1-7 was tested according to the test method of ISO 178; the heat deflection temperature of Examples 1-5 and Comparative Examples 1-7 was tested according to the standard of GB / T 1634-2019; the results are shown in Table 2. The tensile strength and heat deflection temperature of Examples 1-5 are as follows: Figure 1 As shown.

[0045] Table 2 Mechanical properties and thermal stability of Examples 1-5 and Comparative Examples 1-7

[0046] Example Tensile strength / MPa Flexural modulus / GPa Heat distortion temperature / ℃ Example 1 158 8.6 266 Example 2 151 8.0 261 Example 3 155 8.2 263 Example 4 158 8.5 264 Example 5 157 8.3 264 Comparative Example 1 121 6.2 228 Comparative Example 2 98 4.7 112 Comparative Example 3 139 7.5 247 Comparative Example 4 132 7.1 241 Comparative Example 5 135 7.3 246 Comparative Example 6 118 5.8 221 Comparative Example 7 147 7.9 242 Comparative Example 8 127 6.8 234 Comparative Example 9 115 5.6 218 Comparative Example 10 156 7.8 251

[0047] From Table 2 and Figure 1It can be observed that Comparative Example 1 uses unmodified chopped glass fibers. The surface of the unmodified glass fibers only contains inorganic hydroxyl groups and lacks a polydopamine active coating layer. Its interfacial compatibility with the non-polar polyphenylene sulfide matrix is ​​extremely poor, and it cannot form an effective interfacial bridge with the maleic anhydride grafted onto the polyphenylene sulfide. During extrusion processing, not only is glass fiber agglomeration and uneven dispersion prone to occur, but interfacial debonding also occurs. Stress cannot be effectively transferred from the matrix to the glass fiber reinforcement phase, resulting in a significant decrease in the material's load-bearing capacity. Simultaneously, voids and stress concentration defects easily form at the interface, further weakening the material's mechanical and heat resistance properties. Comparative Example 2 removes the modified glass fibers, resulting in a decrease in mechanical properties and thermal stability. This is because the modified glass fibers are the core reinforcement phase, forming a continuous load-bearing network within the polyphenylene sulfide matrix. After removing the modified glass fibers, the material loses the structural support of fiber reinforcement and relies solely on the polyphenylene sulfide matrix and a small amount of powder filler for basic performance. It cannot withstand high loads, and the material's thermal deformation behavior is no longer constrained by the glass fiber network, making it prone to deformation at high temperatures. Comparative Example 3 used unmodified silica fume. Unmodified silica fume has a strong surface polarity, resulting in poor compatibility with non-polar polyphenylene sulfide (PPS). It is prone to agglomeration, failing to disperse uniformly and form an effective filling and reinforcing effect. Agglomerated silica fume particles also become stress concentration points in the matrix, easily inducing microcracks under external forces, leading to a decrease in the material's mechanical properties. Furthermore, it cannot effectively restrict the molecular chain movement of the matrix at high temperatures, thus reducing the material's heat distortion temperature. Comparative Example 4 removed the modified silica fume, resulting in a decrease in its performance. This is because modified silica fume, as an inorganic powder filler, can fill the gaps between the PPS matrix and the glass fiber network. It not only improves the material's rigidity and density through a filling effect but also induces heterogeneous nucleation in the matrix, refines the spherulite structure, and improves the material's crystallization uniformity. Simultaneously, it forms a synergistic reinforcing effect with modified glass fibers, further optimizing the material's mechanical and heat resistance properties. In Comparative Example 5, styrene was not added during the preparation of polyphenylene sulfide grafted with maleic anhydride. Styrene is a highly efficient comonomer for the grafting reaction of polyphenylene sulfide and maleic anhydride. Through copolymerization with maleic anhydride, it can significantly improve the grafting rate and grafting stability of maleic anhydride on the polyphenylene sulfide molecular chain. The absence of styrene monomer leads to a decrease in the grafting rate of maleic anhydride, resulting in a significant weakening of the interfacial compatibility effect. This makes it impossible to effectively bridge the polyphenylene sulfide matrix and inorganic filler, reducing stress transfer efficiency and making the interface prone to debonding under external force. At the same time, the reduced dispersibility of the filler makes it easy to form agglomeration defects, resulting in a simultaneous decrease in the mechanical properties and heat resistance of the material.Comparative Example 6 uses maleic anhydride instead of polyphenylene sulfide grafted maleic anhydride. Maleic anhydride is a small-molecule polar monomer and cannot bridge the compatibility between the polyphenylene sulfide matrix and the inorganic filler. Moreover, maleic anhydride is prone to volatilization, decomposition and self-polymerization in the high-temperature environment of twin-screw extrusion and injection molding. It not only fails to form an effective bond at the interface between the matrix and the filler, but also forms processing defects such as bubbles and micropores in the matrix, becoming stress concentration points and weakening the mechanical properties of the material. At the same time, the loss of interfacial bonding force means that the inorganic filler cannot effectively restrict the high-temperature movement of the matrix molecular chains, and the heat distortion temperature of the material is significantly reduced.

[0048] Comparative Example 7 removed nano-hexagonal boron nitride. Nano-hexagonal boron nitride is a sheet-like nanofiller with excellent rigidity, high-temperature resistance, and thermal conductivity. When uniformly dispersed in the polyphenylene sulfide matrix, it can improve the basic mechanical properties of the material through the nano-reinforcement effect. At the same time, its sheet-like structure can form an interlaced rigid network with modified glass fibers, restricting the movement of polyphenylene sulfide molecular chains at high temperatures and increasing the heat distortion temperature of the material. After removing this component, the material lost the synergistic reinforcement and heat resistance of the nanofiller, and the resistance to movement of matrix molecular chains at high temperatures decreased, resulting in a decline in resistance to deformation. Comparative Example 8 removed the composite antioxidant, and the performance of the material decreased. The composite antioxidant is a compound system of hindered phenolic primary antioxidant and phosphite auxiliary antioxidant. Through synergistic action, it can effectively inhibit the thermo-oxidative degradation of polyphenylene sulfide resin during the high-temperature processing of twin-screw extrusion and injection molding, avoiding the problems of polyphenylene sulfide molecular chain breakage and molecular weight reduction. In Comparative Example 9, modified glass fibers were added together with premixed materials such as polyphenylene sulfide resin from the main feed port of a twin-screw extruder. The performance of the material was reduced across the board. This is because the main feed port of the twin-screw extruder is located at the very front of the equipment. After the modified glass fibers are added from the main feed port, they will pass through the strong shearing and kneading section of the extruder throughout the process. This causes the modified glass fibers to be over-shorn, resulting in severe fiber breakage and loss of their reinforcing effect. At the same time, the over-broken modified glass fibers are prone to agglomeration in the matrix, forming a large number of stress concentration defects, which further weakens the mechanical properties of the material. Moreover, the short-cut glass fibers cannot form a continuous rigid network, which cannot effectively restrict the molecular chain movement of the matrix at high temperatures. The heat distortion temperature of the material also decreased. The performance of Comparative Example 10 also showed a slight decrease. The core reason is the variable mold temperature process in the example, which can raise the mold cavity temperature to 150°C during the injection molding stage, significantly improving the fluidity of the polyphenylene sulfide melt, ensuring complete melt filling, improving the density of the product, and providing a sufficient temperature environment for the crystallization process of polyphenylene sulfide, thus improving the uniformity of crystallization. The subsequent instantaneous cooling process can quickly refine the spherulite size, reduce the internal stress of the product, and avoid molding warpage and defects. However, when injection molding at a constant mold temperature of 130°C, the melt fluidity is insufficient during the molding stage, and the product is prone to incomplete filling and insufficient density. At the same time, the temperature control during the crystallization process is uneven, which easily generates large-sized spherulites, resulting in higher internal stress in the product and a slight decrease in the mechanical properties and heat distortion temperature of the material.

[0049] Experiment Example 2: Aging Resistance Test

[0050] The sample was placed in an aging test chamber, the temperature was set to 200℃, and it was baked continuously for 1000h. After being taken out and cooled to room temperature, its tensile strength and flexural modulus after aging were tested again. The results are shown in Table 3.

[0051] Table 3 Aging resistance of Examples 1-5 and Comparative Examples 1-8

[0052] Example Tensile strength after aging / MPa Flexural modulus after aging / GPa Example 1 142 7.8 Example 2 134 7.2 Example 3 137 7.3 Example 4 140 7.6 Example 5 138 7.5 Comparative Example 1 92 4.5 Comparative Example 2 68 2.6 Comparative Example 3 109 5.7 Comparative Example 4 101 5.2 Comparative Example 5 103 5.4 Comparative Example 6 86 3.4 Comparative Example 7 122 6.3 Comparative Example 8 99 3.8

[0053] Table 3 shows that Comparative Example 1 exhibits a significant performance degradation. The unmodified glass fiber lacks a stable interfacial bond with the polyphenylene sulfide matrix, resulting in numerous voids and internal stress defects at the interface. During thermo-oxidative aging, oxygen easily penetrates the material through these defects, accelerating the oxidative degradation of the matrix resin and further weakening the interfacial bond. This leads to severe interfacial debonding, preventing effective stress transfer between the matrix and glass fiber, resulting in a drastic decline in the material's mechanical properties. Comparative Example 2, without modified glass fiber, lacks the rigid support and protective barrier of the fiber network. During long-term thermo-oxidative aging, the matrix resin undergoes comprehensive oxidative degradation, with continuous chain breakage leading to a significant decrease in molecular weight and loss of load-bearing capacity. Furthermore, the unrestricted matrix is ​​prone to irreversible deformation at high temperatures, ultimately resulting in a decline in mechanical properties after aging. Comparative Example 3, without any modification to the silica fume, exhibits poor interfacial compatibility with the polyphenylene sulfide matrix, failing to form a stable interfacial bond. During long-term high-temperature aging, oxidative degradation easily occurs at the interface, leading to interfacial debonding and the silica fume losing its reinforcing and filling effect on the matrix. Simultaneously, the unmodified silica fume tends to agglomerate within the matrix, and the resulting defects accelerate oxygen penetration and microcrack propagation, further exacerbating material aging and deterioration. Comparative Example 4, without the addition of modified silica fume, results in decreased material density and more internal micropores. Oxygen more easily penetrates the material, accelerating matrix oxidative degradation. Furthermore, the loss of the reinforcing and filling effect of silica fume reduces the material's rigidity, making it more prone to performance degradation during aging. Comparative Example 5, which did not add styrene during the preparation of polyphenylene sulfide grafted with maleic anhydride, resulted in a low grafting rate, failing to construct a stable interfacial bridging structure between the matrix and the inorganic filler, leading to weak interfacial bonding. During long-term thermo-oxidative aging, the weakly bonded interface is highly susceptible to oxidative degradation, causing interfacial debonding. The inorganic filler loses its force transmission function with the matrix, and interfacial defects accelerate oxygen penetration, further exacerbating the overall aging and degradation of the matrix, ultimately resulting in a significant decrease in the mechanical properties of the aged material. Comparative Example 6 replaced polyphenylene sulfide with maleic anhydride. Maleic anhydride is a small-molecule polar monomer, unable to construct a stable interfacial bonding structure. Furthermore, during high-temperature processing, it leaves a large number of small-molecule byproducts and bubble defects in the matrix. During long-term thermo-oxidative aging, these small-molecule residues become initiating points for thermo-oxidative degradation, accelerating the free radical chain oxidation reaction of the matrix resin. Simultaneously, the failed interface undergoes complete debonding, the inorganic filler loses its reinforcing effect, and oxygen rapidly penetrates into the material through interfacial defects and bubbles, leading to matrix degradation. In Comparative Example 7, without the addition of nano-hexagonal boron nitride, the oxygen barrier capacity and thermal conductivity of the material decreased, and the rate of thermo-oxidative degradation of the matrix was slightly accelerated, resulting in a slight decrease in mechanical properties after aging.In Comparative Example 8, without the addition of composite antioxidants, polyphenylene sulfide undergoes uncontrolled thermo-oxidative degradation in a long-term high-temperature environment. The molecular chains continue to undergo oxidative chain breakage, the molecular weight of the matrix decreases significantly, and the basic mechanical properties of the material are destroyed. At the same time, the small molecule byproducts generated by degradation further accelerate the aging chain reaction, forming a vicious cycle, which ultimately leads to a significant decline in the mechanical properties of the material after aging.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a modified sealing material based on polyphenylene sulfide, characterized in that, Includes the following steps: Polyphenylene sulfide resin, hexagonal boron nitride, calcium pimecronate, and a composite antioxidant are mixed to form a premix. The premix, polyphenylene sulfide-grafted maleic anhydride, modified silica fume, and modified glass fiber are added stepwise to an extruder, extruded, water-cooled, pelletized, and dried to obtain modified polyphenylene sulfide granules. The modified polyphenylene sulfide granules are melt-plasticized and injection-molded to obtain the modified sealing material. The polyphenylene sulfide-grafted maleic anhydride is obtained by grafting maleic anhydride onto polyphenylene sulfide. The modified silica fume is obtained by modifying silica fume with a silane coupling agent. The modified glass fiber is obtained by modifying glass fiber with polydopamine.

2. The method for preparing a polyphenylene sulfide-based modified sealing material according to claim 1, characterized in that, The modified sealing material is prepared as follows: the polyphenylene sulfide resin, the hexagonal boron nitride, the calcium pimecronate, and the composite antioxidant are added to a mixer and mixed to form a premix; a co-rotating parallel twin-screw extruder is used, the premix is ​​added from the main feed port, the polyphenylene sulfide grafted maleic anhydride and the modified silica fume are added from the first side feed port, and the modified glass fiber is added from the second side feed port; the extrudate is cooled in a water tank, dried by an air knife, granulated, and vacuum dried to obtain the modified polyphenylene sulfide granules; the modified polyphenylene sulfide granules are fed into an injection molding machine, heated during injection molding, and then cooled to obtain the modified sealing material.

3. The method for preparing a modified sealing material based on polyphenylene sulfide according to claim 1, characterized in that, The modified glass fiber is prepared as follows: chopped glass fiber is placed in a muffle furnace and calcined at 400℃-450℃ for 2 hours. After cooling, it is immersed in dilute hydrochloric acid for ultrasonic treatment, washed until neutral, and dried to obtain activated glass fiber. Deionized water is added to a reaction vessel, and tris(hydroxymethyl)aminomethane is added and stirred to dissolve to prepare a buffer solution. The activated glass fiber is immersed in the buffer solution, dopamine hydrochloride is added, and after stirring and reacting, it is washed and dried to obtain the modified glass fiber.

4. The method for preparing a polyphenylene sulfide-based modified sealing material according to claim 1, characterized in that, The modified silica fume is prepared by adding the silica fume to an ethanol-water mixed solvent and ultrasonically dispersing it to form a suspension; adding KH-550 dropwise to the suspension, stirring and refluxing in a water bath, washing and drying, grinding and sieving to obtain the modified silica fume.

5. The method for preparing a polyphenylene sulfide-based modified sealing material according to claim 1, characterized in that, The preparation method of polyphenylene sulfide grafted maleic anhydride is as follows: maleic anhydride and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane are added to styrene and stirred to obtain a mixed solution; polyphenylene sulfide and ethylene bis-stearamide are put into a high-temperature cold mixer, the mixed solution is sprayed onto the surface of powder, and then mixed and allowed to stand for aging to obtain a mixture; the mixture is put into a co-rotating parallel twin-screw extruder, the extruded strip is water-cooled and air-dried, then pelletized and dried to obtain polyphenylene sulfide grafted maleic anhydride.

6. The method for preparing a polyphenylene sulfide-based modified sealing material according to claim 1, characterized in that, The composite antioxidant includes antioxidant 1010 and antioxidant 168.

7. A modified sealing material based on polyphenylene sulfide, characterized in that, The raw materials for preparation include polyphenylene sulfide resin, nano-hexagonal boron nitride, calcium pimecronate, polyphenylene sulfide grafted maleic anhydride, modified silica fume, modified glass fiber, and composite antioxidant; the modified sealing material is prepared by any one of the preparation methods of claims 1-6.

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